Throw-in thermocouple for basic oxygen furnace



United States Patent O 3,508,976 THROW-IN THERMOCOUPLE FOR BASIC OXYGENFURNACE Kenneth B. Parker, Jr., Norristown, Pa., assignor to Leeds &Northrup Company, Philadelphia, Pa., a corporation of Pennsylvania FiledDec. 20, 1965, Ser. No. 514,961 Int. Cl. H01v 1/04 U.S. Cl. 136-234 7Claims ABSTRACT F THE DISCLOSURE The present invention relates to anexpendable immersion temperature-sensing assembly of the throw-in typeand has for an object the provision of an expendable immersiontemperature-sensing assembly adapted to be thrown into a bath of moltensteel in a `basic oxygen furnace to measure the temperature thereof.

The basic oxygen furnace due to its tremendous eciency enables steel tobe produced at a much faster rate than in furnaces of the open hearthtype. However, basic oxygen furnaces present a more diflicult problemfor temperature measurement of the bath than the open hearth type offurnace. Expendable immersion thermocouples were first introducedcommercially for the measurement of bath temperatures in open hearth andelectric furnaces in 1958. Examples of such expendable immersionthermocouples are disclosed and claimed in Mead Patents 2,999,121 and3,038,951, Moore Patent 3,024,295, Parker Patent 3,048,642 and Robertsonet al. Patent 3,055,961. Such expendable thermocouples normally areintroduced into the furnace by a manipulator or handle of rigidconstruction. When using this type of manipulator to insert anexpendable immersion thermocouple into a basic oxygen furnace it isnecessary to stop the oxygen blast and tilt or position the furnace sothat an operator can immerse the expendable type thermocouple forobtaining a temperature measurement. In view of the fact that the totaltime for steel production in a basic oxygen furnace runs from about 30to 45 minutes, this means that a delay of three or four minutes toobtain a temperature reading becomes a very important percentage of theoverall production time, and hence, becomes a relatively expensivereading. In view of this, various types of throw-in expendable immersionthermocouple assemblies have been developed for obtaining a quicktemperature measurement in a basic oxygen furnace, without the necessityof `withdrawing the oxygen lance and tilting or repositioning thefurnace. Examples of such throw-in assemblies are disclosed in aco-pending application Ser. No. 446,000, led Apr. 6, 1965 by Louis R.Jones, J r., now abandoned in favor of continuation application Ser. No.796,258, tiled Dec. 9, 1968. and in Canadian Patent No. 681,508, issuedMar. 3, 1964.

Since the distance to the surface of the bath with the furnace inupright position is in the order of 30 to 40 feet in a basic oxygenfurnace, the aforementioned throwin expendable thermocouple devicesutilize relatively long lengths of leadwire cable, for example, in theorder of 50 feet. In the preferred forms of throw-in thermocouples, thecoil of lead wire is carried by a support which permits the lead vwireto pay out and avoid tangling when the unit is dropped or thrown intothe furnace. As disclosed in the aforesaid application, the preferredform of support for the coil of lead wire comprises a cardboard tube onwhich the lead Wire is coiled. The cardboard tube also providesprotection for the lead wire near the expendable thermocouple unit as itpasses down through the furnace. The lower end of the cardboard tube isprovided with a metal weight so as to cause the expendable thermocoupleunit to be immersed in the molten metal bath. However, due to thebouyancy of the cardboard tube, a relatively heavy weight is required inorder to move the expendable thermocouple unit below the surface of thebath. Accordingly, the present invention provides for automaticseparation of the weight and cardboard tube at the time when or beforethe weight enters the bath, so as to reduce the buoyancy of theassembly.

In accordance with the present invention, there is provided anexpendable immersion temperature-sensing assembly adapted to be throwninto a molten bath to measure the temperature thereof such, for example,as a bath of molten steel in a basic oxygen furnace. Such assemblyincludes weight structure having a density greater than that of thematerial of the molten bath, the weigh sructure having a cavity open atthe immersion end thereof. A body structure including material havingboth heat nsulating and electrical insulating characteristics is fittedinto the open end of the cavity to form a plug therefor. A refractoryprotected temperature-sensing device is supported by the body structureand projects outwardly therefrom away from the cavity. The end of :acable comprising heat insulated lead Wires extends into the weightstructure from the opposite end thereof and is electrically connectedwithin the cavity to the temperature-sensing device. A cardboard tube isloosely fitted onto the end of the weight structure into which the leadwires extend. There is further provided heat softening means releasablysecuring the weight structure to the cardboard tube. The heat softeningmeans has the Characteristic of melting as the immersion end of theWeight structure enters the furnace which is a zone at elevatedtemperature thereby effecting separation of the weight structure fromthe cardboard tube so as to reduce the buoyancy of the assembly thatpenetrates the bath. The heat softening means, in the preferred formthereof, comprises a plastic tape which holds the cardboard tube to theweight structure for a time; however, it permits separation before or atthe time the temperature sensing device hits the bath, separation of thecardboard tube from the weight structure permitting the latter to sinkbelow the surface of the molten bath uneeced by the buoyancy of thecardboard tube. At the same time the cardboard tube provides protectionfor the lead wire as it enters the furnace and particularly at the pointwhere the cable enters the weight.

For further objects and advantages of the present invention, and for amore detailed description thereof, reference is to be had to thefollowing description taken in conjunction with the accompanyingdrawing, which is an elevational view, partly in section, of anexpendable thermocouple assembly embodying the present invention.

Referring to the drawing there has been illustrated an expendablethermocouple assembly 1t) embodying the present invention andparticularly suited for measuring the temperature of the molten bath ina basic oxygen furnace. The assembly 10' includes a pair of dissimilarthermocouple elements 11 and 12 connected together at one of their endsto form a hot or measuring junction 13 for the thermocouple. Theserially connected thermocouple elements 11 and 12 are inserted in arefractory protective tube 14 which may be made of silica, quartz ofVycoL The opposite ends of the refractory tube 14 are supported within abody structure 16 which may be made from refractory cement, ceramic,wood or other material having both heat insulating and electricalinsulating characteristics such, for example, as disclosed in theaforesaid Parker Patent No. 3,048,642 or the other above-mentioned U.S.patents, or in the copending application Ser. No. 193,706, filed May 10,1962 by Davies, issued Jan. 17, 1967 as U.S. Patent No. 3,298,874. Afusible protective cap 17 encloses the refractory protected thermocoupleand is mounted on the body member 16. It will be seen that theexpendable thermoeouple unit, as thus far described, is similar to suchunits disclosed in the aforesaid U.S. patents and applications. Thethermocouple elements 11 and 12 will normally be made from noble metalmaterial and thus, in order to use short lengths of these elements,their ends opposite the hot junction 13 are connected within the body 16to short lengths of extension lead wire 19 and 20V which extend from theopposite end of the body member 16 for connection to a measuringcircuit.

As may be seen in the drawing the body member 16 is tapered and isadapted to be received in the open end of a cavity 18a Within a metalweight structure 18. The end of the weight structure 18 which receivesthe expendable thermocouple unit is referred to as the immersion end asthat is the end which enters the molten bath first. In order to protectthe thermocouple assembly during storage, shipment, and when it isdropped into the furnace the immersion end of the weight structure 18 isprovided with three projecting feet 18b spaced equidistantly about thethermocouple unit.

The lead wire extensions 19 and 20 are adapted to be connected bycrimped connectors 21 and 22 to corresponding lead wires 23 and 24 whichare a part of heat insulated lead wire cable 25. As pointed out in theaforementioned Jones application, the cable 25 is long and flexible sothat it may be coiled in various shapes and includes an outer casingwhich is solidly packed with asbestos insulation or equivalentinsulation including rubber compositions, and a heavy paper wrappingsutiicient to protect the lead wires 23 and 24 during the time requiredto record a temperature measurement. In order to keep the lead wires 23and 24 from contacting each other within the cable 25, such lead wiresare provided with individual electrical insulation elements 23a and 24a,respectively, which may be color coded or otherwise marked to identifypolarity of the thermocouple. The cable 25 is adapted to extend througha passage 18C of the weight structure 18 at the end opposite theimmersion end. The passage 18e is only slightly larger at its insidediameter than the outside diameter of the cable 25. Thus, it will beseen that the cable 2S and the body member 16 effectively plug theopposite ends of the cavity 18a and prevent entry'of molten metal intothe area surrounding the crimped connectors 21 and 22.

The metal weight 18 is preferably made from steel or cast iron so thatthe weight structure will have a density greater than that of the moltenbath. The upper end of the weight structure 18 (as shown) is providedwith a reduced diameter 18d terminating in a shoulder 18e against whichthe lower end of the cardboard tube 26 abuts. The outside diameter ofthe portion 18d is slightly less than the inside diameter of thecardboard tube 26 and the depth of the shoulder 18e correspondsapproximately to the wall thickness of the cardboard tube 26. Thedimensions of these parts are so selected that the cardboard tube willloosely fit onto the weight structure 18. The cardboard tube 26 isadapted to be releasably secured to the weight structure 18 by heatsoftening means such, for example, as a plastic tape 27. The plastictape 27 is adapted to overlap the joint between the metal weight 18 andthe adjacent end of the cardboard tube 26 and may be applied thereto insections or it may extend completely around the tube 26. The tape 27 hasthe characteristic of melting as the weight structure 18 enters thefurnace thereby effecting separation of the weight structure from thecardboard tube 26 so as to reduce the buoyancy of the portion of theassembly which enters the bath.

In one embodiment of the invention the Weight structure 18 had a Weightof about iive pounds, two ounces and an outside diameter of about 31/2inches and a diamv eter at 18d of about 37/32 inches. The cardboard tube26 had a wall thickness of about 1A; inch and an inside diameter ofabout 3%, inches. The tape 27 consisted of black, plastic electricaltape 1/2 inch wide.

While in the preferred form of the invention the heat softening means 27for releasably securing the weight structure 18 to the cardboard tube 26is an adhesive plastic tape, it is to be understood that otherequivalent heat softening or heat destructible means may be utilized andare intended to be generically included by the language melting or thelike as used in the claims. For example, the heat softening means maycomprise adhesive securing the end of the cardboard tube 26 to theshoulder 18e, such adhesive having a heat softening point substantiallybelow the temperature of the molten metal bath.

Or, for example, the tube itself may have a section of wall near theassembly of lesser cross section and the tube made of a heat-softenablematerial so that it will quickly melt in the region of lesser crosssection and separate the tube from the assembly. Thus, my inventionembraces broadly the concept of a support for an extended length of leadWire preferably in coil form, and preferably in a single layer helicalcoil within a tube, which, by reason of the heat in the vicinity of themolten bath, is during its travel toward the molten bath severed fromthe weighted assembly, thus to avoid the effect of buoyancy of the tubewhether vented or not.

Alternatively, the means for releasably securing the weight structure tothe cardboard tube may comprise other materials such as metal and thelike which are fusible, combustible, or melt at temperaturessubstantially below the temperature of the molten bath. Examples of suchmaterials are solder and other equivalent low temperature metals as Wellas plastic bands and the like. While the tube 26 has been described asbeing made of cardboard it is to be understood that the tube 26- may bemade of other material. The lead wires in the cable 25 may be ofcompensating materials as well known in the art or they may be ordinarycopper lead wires as disclosed in the aforesaid copending application ofJones. The term coil as used in the claims is defined generically asincluding a spiral, helix, hank, accordion fold, wad or any otherpredetermined arrangement of the supply of heat insulated lead wirecable.

From the foregoing it will be seen that the expendable immersiontemperature-sensing assembly 10 includes a weighted subassemblycomprising a temperature-sensing device such as an expendablethermocouple unit, and weight structure |18 which imparts to theweighted subassembly a density greater than that of the molten materialthe temperature of which is to be measured to assure sinking of thesubassembly into the molten material. The lead Wires 23 and 24 ofextended length are adapted to be connected to one end of thetemperature-sensing device and are supported by means secured to theweighted subassembly, the last named means being separable from theWeighted subassembly in response to the heat in the vicinity of themolten material thereby to separate the same from the weightedsubassembly so that the density of the Weight structure will sink thetemperature-sensing device into the molten material during thetemperature measuring period.

It is to be understood that the present invention is not limited to thespecific arrangements described and illustrated herein but furthermodifications thereof may be made within the scope of the appendedclaims.

What is claimed is:

1. An expendable immersion temperature-sensing as- Vsembly adapted to bethrown into a bath of molten material to measure the temperature thereofcomprising:

weight structure having a density greater than that of the material ofthe molten bath,

a temperature-sensing device supported in protruding relation at an endof said weight structure, heat-insulated lead wires extending into saidLweight structure and electrically connected to said temperature-sensingdevice,

a tube loosely iitted onto said weight structure and supporting saidlead wires, and

heat softening means releasably securing said weight structure to saidtube, said heat softening means having the characteristic of melting asthe assembly enters a zone at elevated temperature thereby effectingseparation of said weight structure from said tube so as to reduce thebuoyancy of the portion of said assembly which enters the bath of moltenmaterial.

2. An expendable immersion temperature-sensing assembly according toclaim `1 wherein said heat softening means comprises plastic adhesivetape overlapping the joint formed between said tube and said weightstructure.

3. An expendable immersion temperature-sensing assembly according toclaim 1 wherein said heat softening means comprises a ring of materialextending around the lower end of said tube and overlapping the jointbetween said end of said tube and said weight structure.

4. An expendable immersion temperature-sensing assembly according toclaim 1 wherein said temperaturesensing device comprises a refractoryprotected thermocouple device.

5. An expendable immersion temperature-sensing assembly according toclaim 1 -wherein said tube is a cardboard tube and said heat insulatedlead wires are coiled in the form of a helix within said cardboard tubeand engage the inside circumference of said tube so as to allow the leadwires to pay out freely and without tangling when said assembly isdropped into the bath of molten material.

6. In an expendable immersion temperature-sensing assembly, a weightedsubassembly including a temperaturesensing device and weight structureimparting to said weighted subassembly a density greater than that ofthe molten material the temperature of which is to be measured to assuresinking of said subassembly in the molten material, and

means secured to said weighted sub-assembly for supporting an extendedlength of lead wire connected at one end to said temperature-sensingdevice, Said last-named means being separable from said weightedsubassembly in response to the heat in the vicinity of the moltenmaterial thereby to separate the same from said weighted subassembly s-othat the density of said weight structure will sink saidtemperaturesensing device into the molten material.

7. The method of supporting an extended lentgh of lead wire connected atone end to a temperature-sensing device during the time interval thatdevice and a weighted structure forming a part of its assembly istraveling from a point in spaced relation to a bath of molten material,which comprises:

disposing the extended length of lead wire about a support aixed to saidassembly and subsequently applying heat from the vicinity of said moltenmaterial to separate the support from said assembly while said assemblyis traveling toward said molten material for sinking of the same intothe molten material.

References Cited UNITED STATES PATENTS 3,359,801 12/1967 IRasmussen.

VVINSTON A. DOUGLAS, Primary Examiner M. J. ANDREWS, Assistant Examiner

